The current tendency for better living conditions has given a rise to the demand for air conditioning, as well as for hot water running service and runing service of cooling water for cooling machines In particular, buildings designed for business activities consume much energy because of cooling load which is increased as a result of heat generation from various machines such as computers and other office machines. In order to reduce the level of peaks of thermal load and electricl power consumption, while attaining a higher economy by utilization of electricl power available at midnight, buildings intended for business use and other large-scale buidings are equipped with heat accumulating water pools or tanks. In some cases, area-wide air-conditioning systems are adopted for conditioning air in a wide area including a plurality of buildings, by employing a water pool or tank system.
Usually, a heat accumulation water tank, i.e., heat accumulation tank, is sectioned into a plurality of water tanks by means of partition walls, for the purpose of improving the heat accumulation effect through smoothing the circulation of water in the tank system and for the purpose of attaining a higher strength of the tank. In order to efficiently conduct air conditioning by making use of water in the heat accumulation tank system, it is necessary that the amount of water to be heated or cooled is suitably controlled in accordance with the seasonal variation in the demand for air conditioning. To cope with such a demand, the water tanks of a heat accumulating tank system are grouped into a plurality of blocks each including one or more water which are mutually connected, the adjacent blocks being communicated with each other through communication passages which can be opened and closed as desired. In operation, the communication passages are selectively opened and closed so that these blocks of water tanks are selectively put into practical use in such a manner that only a single block is used or a plurality of blocks are used in combination, thereby optimizing the amount of water to be heated or coled for the purpose of air conditioning.
It is also to be pointed out that the heat accumulating tank system has to be periodically drained for the purpose of inspection of the interior and replacement of water. Preferably, this is conducted by draining some of the blocks while other blocks are operating under ordinary operating conditions, so that the successive blocks of tanks are sequentially drained and inspected. The communication passages between the blocks have to be opened and closed also for this purpose.
Conventionally, the means for seelectively opening and closing the communication passage employs a mechanical valves such as a slide-type shut-off valve or a butterfly valve. These valves are usually operated by a valve actuator which is installed on the upper side of the tank so as to be moved up and down or rotated thereby opening and closing the communication passage.
The valve mechanism used conventionally thus requires a large space for accomodating a valve actuating mechanism which is installed on an upper part of the tank. In addition, maintenance work has to be executed frequently for maintaining good conditions of the valve and the valve actuating mechanism. For instance, in the case of a slide-type valve, it is necessary to lift the valve member to open the communication passage, so that a space large enough to accommodate the valve member has to be preserved on the upper side of the heat accumulating tank. On the other hand, when a butterfly valve is used, the have shaft has to be extended upward to project from the tank and a valve operating handle has to be attached to the extended portion of the valve shaft. Obviously, the thermal load on the air conditioner is increased as the scale of the building is increased, and the heat accumulating tank also becomes greater. This requires the size of the of the valve in the communication passage and, hence, of the mechanism for actuating the valve, with the result that a large space is required for the maintenance work. In consequence, the area for lent on the floor immediately above the heat accumulating tank or the area of the machine room or parking area is reduced uneconomically.
The conventional valve mechanisms suffer a problem in regard to the durability. Namely, the temperature of the water in the heat accumulating tank is usually maintained at about 5.degree. to 10.degree. C. during cooling of air and at about 50.degree. to 60.degree. C. during heating. The valve member, valve seat and seal members of the valve mechanism are left in water for a long period of time, so that the problems are caused such as deterioration of the valve member and the sealing member, rusting of movable parts, stick of the sealing member, and leak through the valve. In consequence, works such as renewal of the sealing members and maintenance of the sliding parts of the valve have to be conducted rather frequently. These works are laborious and require much time and money. In some cases, water pooled in the tank system has to be wasted.